Networks design is important in deciding the performance of the network during fault conditions. Traditionally, the ease of operation, administration, management and provisioning (OAMP) of ring based network design of transport networks like Synchronous Digital Hierarchy (SDH) and Synchronous Optical Network's (SONET) have triggered extensive research of similar mechanisms for the packet network.
The ring based network design like Unidirectional Switch Ring (UPSR) and Bidirectional Line Switch Ring (BLSR) yields a number of advantages, including simplified management and control of the network, and fast restoration mechanisms upon link or node failure occurrence. The design of a given arbitrary topology in the form of a set of interconnected rings reduces the overall network connectivity and hence may limit the number of distinct cables that carry working fibers in the final network layout. With reduced number of cables in the system the overall network cost may also be reduced. Due to these and other advantages, it is not surprising that ring based network designs are often preferred to other network topologies.
The new networks are required to have both high capacity and high survivability. In a ring structure there are two ways to send traffic, clockwise or counter-clockwise. This means that the traffic can be sent even if a single link or node breaks down, by using the opposite direction of the ring. The rings are so called self healing rings (SHR) where some capacity is unused until the event of a link or node failure. The technology is based on SDH standard for optical transmission. Newer packet-based ring standards also behave in similar fashion (for example G.8031)
There have been efficient protection mechanisms for protecting multicast traffic in a mesh or ring topology network utilizing label switching protocols. The label switching technique was developed to expedite the look-up process at each network node as packets travel from a source to a destination. Abstractly, label switching involves attaching a label to a packet that enables the next node (i.e., hop) of the packet to be quickly determined by an intermediate network node that receives the packet. An example for such a label switching protocol is the Multi-Protocol Label Switching (MPLS) protocol.
The existing methods are not deterministic to route a frame (or packet) when a primary path to destination is unavailable due to node/link failure, bandwidth crunch, mis-configuration, etc. Also, there is no provision of primary and secondary (or alternate) path to route the traffic to minimize the switch-over time to enable 50 ms protection switching in a packet network. Furthermore, even though the traffic is provisioned results in increase in the complexity of the network.
Thus there is a need to have a hierarchy of cycles capable of providing 50 ms protection for unicast and multicast traffic. Also, there is therefore a requirement of a network system which allows for better propagation of packets through the network and allows for quick recovery at the time of fault conditions.